This invention relates generally to golf clubs and, in particular, to so-called metal-wood drivers.
Recent developments in golf club design have included improvements in drivers, which are clubs used primarily to strike a golf ball resting on a golf tee. These improvements have resulted in drivers with club heads consisting of a hollow shell usually made of metal, such as steel or titanium. One example of a golf club head consisting of a hollow metal shell is disclosed in U.S. Pat. No. 5,851,160 to Rugge et al. In an effort to obtain better and better performance from these hollow metal-wood drivers, however, golf club manufacturers have increased the head volume from a moderate volume of 250 cubic centimeters as disclosed in Rugge et al. to over 400 cubic centimeters in recent years. The striking face of a metal-wood driver must be of a certain minimum thickness in order to withstand impact forces generated upon impact with a golf ball. Accordingly, as head size increases, less and less material is available for fabricating the crown, sole and skirt of the club head while maintaining the club head of these oversized drivers within acceptable weight limitations.
In U.S. Pat. No. 6,471,604, one golf club manufacturer has suggested a club head having a metallic face bonded to an aft body composed of a non-metal material such as a composite or thermoplastic material. The lightweight plastic rear body enables more metal to be dedicated to the striking face, however, many golfers dislike the impact sound produced by a club having a low resonance, highly damped non-metallic rear body. Moreover, because of the discontinuity between the all-composite or thermoplastic rear body and the striking face, the striking face is not significantly supported by the rear body. Consequently, more material must be dedicated to the striking face itself, thereby canceling out much of the weight savings attributable to the non-metallic rear body.
U.S. Pat. No. 7,008,332 to Liou suggests a metal-wood driver having large apertures in the crown and skirt. The apertures are then covered by a graphite cover that conforms to the crown and skirt portions of the club head. The large aperture in the crown and/or skirt enable more metal to be dedicated to the striking face. Because of the large apertures, however, the striking face is not significantly supported by the crown and/or sole. Therefore, more material must be dedicated to the striking face itself, which cancels out much of the weight savings attributable to the large apertures. Implicitly recognizing the disadvantages of a club head in which the face is unsupported by the crown, the '332 patent discloses one embodiment in which the face is supported by a single rib perpendicular to the face, bisecting the crown aperture. A single perpendicular rib, however, itself produces a stress concentration at the point where it merges with the crown extension behind the face. Moreover, a single rib is easily driven into a first bending mode vibration upon impact of the face with a golf ball. Thus the single perpendicular rib not only provides little support for the face but also dissipates impact energy by its vibrational oscillations, thereby leaving less energy available to be imparted to the golf ball.
Accordingly, what is needed is a club head having crown apertures that are strategically located in areas that are not excited by the crown bending moments induced by ball impact and therefore permit relocation of material from the crown to other areas of the club head without reducing the stiffness of the crown or lowering its natural frequencies.